Radar-controlled guidance system



Nov. 3, 1964 R. MATTHEWS ETAL 3,155,968

RADAR-CONTROLLED GUIDANCE SYSTEM 3 Sheets-Shea?l 1 Filed April 7, 1958 N i www 5 Sheets-Sheet 2 R. MATTHEWS ETAL RADAR-CONTROLLED GUIDANCE SYSTEM Nov. 3, 1964 Filed April 7, 1958 Nov. 3, 1964 R. MATTHEWS ETAL. 3,155,968

RADAR-CONTROLLED GUIDANCE SYSTEM Filed April '7, 1958 3 Sheets-Sheet 3 United States Patent O 3,155,968 RABARHCNTRLUED GUIDANSE SYSTEM Robert Matthews and Ronald ridiomas Albert Howell,

London, England, assgnors to Decca Limited, lirondon, England Filed Apr. 7, i958, Ser. No. 726,820 23 Claims. (El. 3dS- 7) i This invention relates to apparatus for controlling the navigation of a vehicle, such as an aircraft, for making the vehicle travel along a required track or for guiding the vehicle by reference to a predetermined position line.

According to this invention apparatus for controlling the navigation of a vehicle comprises first signal generator means arranged to generate electrical signals representative of the co-ordinates of the instantaneous position of the vehicle, further signal generator means arranged to generate electrical signals deiining a required track in said co-ordinate system, and comparator means for comparing the signals from rst signals generator means with the signals defining the required track to provide an output representative of the distance of the point represented by signals from said iirst signal generator means from the line delined by the output ofsaid further signal generator means.

As will hereinafter be more fully explained, the apparatus is particularly applicable to the controlling of a vehicle such as an aircraft from a radar station employing a primary or a secondary radar system. The signals representative of the co-ordinate position of the aircraft may then be derived from a plan position radar display either manually or automatically by means of an echo follow system described-and claimed in the specication or" patent application No. 678,890 now U.S. Patent 3,120,660.

The output from said comparator means might be displayed at the radar station so that the output information can be transmitted verbally by a radio communication link to the Vehicle. Alternatively the output may be automatically transmitted to the vehicle by a radio communication system. Display means may be provided on the vehicle for displaying the transmitted information or the information may be applied directly to an automatic pilot of the vehicle. The outputs would usually be avail able as voltages and information representative of these voltages may be transmitted over the radio communication system as modulations in any convenient way such as for example the methods employed in telemetering systems.

The vehicle may readily be guided so as to follow the aforementioned required track by controlling the course of the vehicle in such a manner as to keep the determined distance from the course as close as possible to zero. This distance might however be kept at some other selected and possibly varying value if it is required to travel along some other track. More generally if the distance along the required track line is known, by using a straight track line, the 3o-ordinate position of the vehicle can be obtained and the apparatus might be used for determining and transmitting the position of a vehicle anywhere within the coverage area of a radar station. lt will be understood therefore that reference to a required track line does not necessarily mean that the vehicle is to be made to follow along this line but includes more generally navigational control by reference to such a line.

In apparatus for use when the required track in plan position is a straight line, the aforesaid iirst signal generator means may be arranged to generate two signals representative in Cartesian co-ordinates of the plan position of the vehicle and said further signal generator means may be arranged to provide two signals representative of the co-ordinate position in the same co-ordinate system of a point on the required track and also a signal or sig- 3,l55,%3 laterited Non'. 3, i964 ice nals representative of the angular direction of the required track, and said comparator means may comprise means for determining the diiierences between the outputs from said first signal generator means and the corresponding outputs from said further signal generator means representative of said point, resolving means controlled by or in accordance with the signal or signals representative of the angular direction ofthe required track arranged to resolve said differences into components along and transverse to the track and combining means to combine the resolved components transverse to the track to provide an output representative of the distance of the vehicle from said track. means to combine resolved components along the track to provide an output dependent on the distance of the vehicle along said track from said point. It will be appreciated that, if the distance to any other point along the required track is required, it may be obtained by simple subtraction or addition which may readily be effected electrically. Thus an output signal can be provided representative of the distance of the vehicle along the track from any selected point such as, for example, the starting point or the final destination.

The arrangement described in the previous paragraph is particularly convenient for use with radar systems in which there is provided a cathode ray display tube with fixed deliector means for deecting the cathode ray beam in two orthogonal directions and interscan trace generating means of the kind described and claimed in the specication of US. Patent No. 2,849,708, which specification describes apparatus for generating interscan line traces in the intervals between the radar display scans by making use of voltages representative of the position of start of the required interscau line trace and also rate controlling voltages representative of the required rates of scan in the two co-ordinate directions of deflection. Such an interscan line trace may be made curved if desired by use of suitable waveforms for the rate controlling voltages. With radar display apparatus having such an interscan display system, the required track may be displayed as a trace on the screen of the tube and the position control voltages for controlling the position of the start of the interscan line trace may be used as one of the inputs to the comparator means. However, there is no need to display the aforementioned line trace on the screen of the tube although in general it will be most convenient to do so. All that is required is that there shall be available voltages representative of the end or of s-ome particular point on this line and also information about its direction.

ln another arrangement, apparatus for controlling the navigation of a vehicle along a required track comprises electrical waveform generators arranged to generate repetitive synchronised waveform representative of the co-ordinates of the required track of the vehicle signals generator means arranged to generate electrical signals representative of the co-ordinates of the instantaneous position of the vehicle and comparator means for determining the diiferences between the signals representative of the vehicle position and the corresponding co-ordinate instantaneous output signals of said waveform generators at simultaneously occurring instants in the waveform cycles and for providing from said determined differences an output representative of the distance of the vehicle from said line. More particularly, for controlling the navigation of a vehicle along a required track in plan position, the apparatus may comprise two electrical waveform generators arranged to generate repetitive synchronised waveforms representative of the eco-ordinates in plan position of the required track for the vehicle, signal generator means arranged to generate two electrical signals representative respectively of the two co-ordinates of the instantaneous position of the vehicle and two com- There may also be provided combining parator means for determining the differences between the signals representative of the vehicle position and the corresponding co-ordinate instantaneous output signals of said waveform generators 'at'simultaneously occurringinstants in the waveform cycles and for providing from said determineddifferences anoutput representative of the distance of the vehicle'from said line.

The aforementioned comparator means may include pulse sampling demodulators for sampling and storing voltages representativeof the required instantaneous voutputsignals of said waveform generators, means for obtaining ditferenc'e signals having magnitude proportional to the differences 'in the co'ordinate directions between the signals representativev of the vehicle position andl the sampled voltages and resolving and combining means controlled in accordancewith the direction of the track at the point corresponding'to the sampling position for resolving and combining thediilerence signals to provide an output representative of thedistance of the vehicle from said line. The aforementioned resolving andcom'bining means may also be arranged Ato provide anoutput representative of the distance ofthe vehicle along'said track from a 'selected point. A'rate-aiding circuit may be provided for controlling the instant of sampling of said pulse sampling demodulators so that the sampling point traverses along the track at an adjustable rate whichmay be said to correspond to the speed of the vehicle.`

In any ofthe above described arrangements the aforesaid signal generator means' for generating signals representative of the position of the vehicle may comprise manually controlled'voltage generator generating means, for example a vmanually operable sine-cosine Vpotentiometer and manually operable voltage controlling means controlling a voltage applied to the'potentiometer. Alternatively the signal' generator means may comprise a primary `or secondaryradar system and means responsive to the received radar signalsfor' automatically producing voltages representativeof the position ofthe vehicle. For example, for controlling navigation of the vehicle in plan position, the voltages representative of the position of the vehicle may be automatically produced by apparatus as described and vclaimed in the specification of patent application No. 678,890, now U.S. Patent 3,120,660.

Any of the forms of apparatus described above are preferably arranged in combination with a primary or secondary radar system havingva plan position cathode ray tube display and the aforementioned signal generator means' for generating signals representative of the position of the vehicle are arranged to control an electronic marker at said display. A further electronic marker in the form of a line trace may be arranged on said display to represent'the required track.

According to another feature of the invention, apparatus for controlling the navigation of a vehicle from a radar station having a cathode ray display tube with xed defiector means for deflecting the cathode ray beam in two orthogonal'directions comprises a marker system for producing a movable electronic marker on the screen of a tube byapplyingtwoy marker deflection signals of adjustable magnitude to said deiiector means for effecting deflection of the cathode ray beam in the two orthogonal directions, means for producing: signals representative of a position of a'linetrace on saidscreen corresponding to a track to rbe followed by said vehicle, and two` comparator' meansifordetermining the differences between the magnitudes of .each of the two marker deiiection signals and of 4two corresponding signals representative of a point on the line trace and for providing from said predeterminedA differences two outputs representative of the distance of the marker from a point on said line and the distance along the line from-the pointnearest the marker to a datum point. With this arrangement, the marker is positioned on the screen over the response from the vehicle to be controlled and the comparator means will then give two outputsrepresentative of the distance of the vehicle along its required track and the distance off the track.

The following is a description of a number of embodiments of the invention, referencey being made to the accompanying drawings in which:

FIGURE 1 is a block diagram illustrating one form of apparatus for controlling the navigation of a vehicle along a straight line or with reference to a straight line;

FIGURE 2 is a block diagram illustrating another form of the apparatus for controlling a vehicle along a predetermined line or-with reference to a predetermined line;

FIGURES 3 and`4a, b, c and a are explanatory dia-V matically radar apparatus comprising a transmitter It?, a Y

scanning antenna 11 and a receiver 12, the receiver-feeding a display unit l?) which includes a'cathode ray. tubeV 14 on which the radar apparatus provides a vplan posi# tion display. this display unit is of the type known as a fixed coil display in which the cathode ray tube has xed deflector coils to which appropriate detiecting signals are applied to effect scanning of the cathode ray beam and-preferably the deflection scanning system is the type described and claimed in the specication of US. PatentNo. 2,849,708`

in whichinterscan marker lines maybe displayed-on the screen of the tube in the intervals between radar displayscans. Reference may be made-to the. specificationof US. Patent No. 2,839,708 for a further description of such a system, but as explained elsewhere, for example" in the specification ofthe aforementioned patent application No. 678,890, now U.S. Patent 3,120,660, itis not necessary to have a separate waveform generator system for each interscan and there are illustrateduin FIGURE 1 of the accompanying drawings two waveform generators 15, I6 feeding fixed defiector coils T17, 1S for eectin detiection of the beam of the cathode ray tube I4.

The present invention is moreparticularly concerned- If the- With the control of thenavigation of a vehicle. position of the vehicle is determined from the radar display, most conveniently a target marker, for example a small circle, is provided on the screen of the display to` mark the particular vehicie which isto be controlled.V For -this purpose there is provided a target positionsignal generator 20 which produces two direct voltage outputs representative ofl the-coordinate position of the vehicle on the screen of the tube. These voltages might be used directly to control the deflection of the cathode ray beam but preferably they are applied to shift control inputs of the Waveform generators 15, 16 which waveform generators are of the kind comprising a high gain arnpliiierhaving two alternative input and feedback circuits. @ne

input and feedback circuit comprises a resistive' input and a resistive feedback for'the amplifier and thel other comprises a `resistive input and a capacitive feedback; As is well known, such a circuit Would provide a,sa\'- tooth output having a starting point dependent ontne voltage applied to the resistive input of the nrst input and feedback circuit, which input is therefore referred to as the shift control input, and having a slope dependent on the voltage appliedtothe resistive input of the second input and feedback circuit, which input circuit is there;

lfore referred to as the rate of scan input. A fuller description of such waveform generating circuits applied to the detiection of a cathode ray tube for radar appa- In the particular embodiment illustrated,

ratus is given in the speciiication of US. Patent No. 2,994,868. The voltage from the target position signal generator is applied to the shift control inputs of the waveform generators l5, 16 and, if a Zero voltage is applied to the rate of scan control inputs (tor example by interrupting the rate of scan control input) a stationary marker will be produced on the cathode ray display tube. The inputs of the two scanning waveform generators may be modulated in phase quadrature by a small amplitude alternating current so that the spot becomes a small circle. Such a method of marking the position of a selected target on a cathode ray tube is known and is described for example in the specication of patent application No. 695,789, now abandoned. This target position marker thus is formed as one interscan trace on the screen of the display tube The vehicle in the arrangement of FGURE l to be guided along a straight line or with reference to a straight line, which line is delined by two co-ordinates representing a point on the line, conveniently the starting point, and by the direction of the line. Direct voltages representative of the co-ordinates of the starting point of the line are produced by a datum position signal generator 21 and these two voltages are applied respectively t0 the shift inputs of the waveform generators l5, lo to control another interscan marker trace which is also produced in the intervals between the radar display traces. it will be understood that each individual interscan trace may have a much lower repetitive rate than the pulse recurrence frequency of the pulse radar system so that a large number of independent interscan traces may pro vided if required. In FGURE l, switches 22 are illustrated diagrammatically for switching the shift input circuits; these switches would be electronic switches to give the necessary speed of operation and the circuits for producing the radar display scans have been omitted for simplicity. When the datum position inputs are applied to the waveform generators l5, lo, sineand cosine direct voltage signals from a sine-cosine signal generator are applied to the rate of scan inputs of the waveform generators so as to produce a line trace on the screen of the cathode ray tube ld in a direction dependent on the setting of the sine-cosine signal generator 23, which setting is determined by a manual control 2d.

In the arrangement of FIGURE l 4the two signals representative of the position of the start of the line trace and the two signals representative of the target position are fed to subtracting units 27, 28 which determine the differences between the two cO-ordinates representative of these two points, taking due account of the signs (le, the polarities) of the signals. To determine t? e distance of the point represented by the output of the signal gen erator 2L@ from the line defined by the output of the signal generator 2l and the setting o' the manual control 2d, the difference signals from the subtracting units Z7, 2S are resolved by resolvers 29, Sil, which are controlled by the manual control 2d, into components in the direction of and transverse to the line. The two outputs from the resolvers 29, 3d which are representative of distances along the track are combined in a combiner 31, the output of which is displayed on an indicator 32 and the two outputs of the resolvers 29, which are representative of distances transverse to the track are combined in a combiner 33 and displayed on an indicator 3d. The apparatus of FlGURE. l is operated by setting the datum position signal generator Zi and the manual control 2d to define the required track line and by adjusting the target position signal generator (assuming there is no automatic following system) to cause the target marker to follow the movements of the vehicle on the display tube.

lt will be seen that the indicators 32, 3d given a visual indication of the distance of the vehicle along the track and the distance olf the track. lt will readily be apparent that, by suitable choice of the zero indication and direction of movement of the indicator 32, the distance along the track may be measured either from the beginning or from the end or from any required point along the length of the track. The outputs on the indicators 32, 3d may be used for controlling the vehicle verbally by means of a radio communication link to the aircraft. Alternatively one or both of the outputs may be automatically,transmitted to the vehicle by a radio communication system and such an arrangement is indicated diagrammatically in FlGURE 1 where the outputs from the eombiners 3l, 33 are fed to a modulator 35 for modulating a transmitter 36. At the vehicle the signals from the transmitter 36 are received by a receiver 37 and demodulated by a demodulator 3S to feed two indicators 39, itl which give indications corresponding to the indications on the indicators 32, 34 at the radar station. lt is not believed necessary to give any further description of the manner of transmitting the signals since many methods for transmitting such signals are well known, particularly for telemetering purposes. lt will further be appreciated that the outputs from the demodulator 33 might be applied directly to an automatic pilot on the vehicle.

lf the vehicle is required to travel along the straight track delined by the system, then the vehicle is navigated so as to keep to a minimum the distance off the track as indicated by the indicators 343- or ill which indicators will indicate the distance and sense of deviation from the track. it necessary the voltage representative of the deviation may be dil'erentiated with respect to time so that the rate ot change of deviation can be presented, if required, to prevent yawing as the vehicle returns to course. The vehicle might also be navigated along a path different from that defined by the datum position signal generator 2l and the manual control 2d by controlling the vehicle so that the distance ott .the track as indicated by the indicators 34 and/or di) is not zero but some predetermined, and possibly varying, value. lt will be appreciated that in such a case if, for example, the manual control 24 was set to give a position line in Ia North-South direction, the indicators 32, 34 would indicate respectively the two co-ordinates of the position of the vehicle in the North-South and East-West directions and these coordinate indications might be used in any required manner to control the aircraft.

The arrangement may be used not only with a primary radar system, but also with a secondary radar system since, by the use of a transponder in the aircraft, the efective range at which the position of the aircraft may be determined would be greatly increased compared with that possible if the position had to be determined solely by means of a primary radar. Such a transponder would be responsive to radar transmissions but may retransmit the pulses back to the radar station either at the radar frequency or, more preferably, at a frequency in a completely different frequency band. The use of transponders operating in frequency bands different from the radar frequency permits of the Itransponduers in separate chicles operating on dilerent frequencies so that the different responses at the radar station are separable and identifiable. Hence a single radar station may be arranged to control automatically a number of vehicles having transponders operating on different frequencies.

Instead of using a manually operable target position signal generator Ztl, the voltages representative of the position ot' the vehicle may be obtained from a radar set by means of an automatic echo follow system such as, for example, that described and claimed in the aforementioned specilication of patent application No. 678,890.

As previously mentioned, a large number of interscan markers may be provided on one radar display and hence a single radar display may be used for controlling a number of vehicles provided separate target position signal generators Ztl, subtracting means 27, 23. resolvers 29,

r. i 30' and combiners 31, '33 are provided to give the necessary output indications or control signals.

The arrangement described with reference to FIGURE 1 for guiding the vehicle with respect to a straight line may be used for controlling an aircraft along an approach path or for guiding -a ship into a harbour or along a selected channel if a straight line approach path is required. In some cases, however, it is required to guide the vehicle alonga more complex path and in that case the arrangement of FIGURE 2 may be employed which permits of directly determining the deviation of a vehicle notonly from straight but also from non-straight course lines. v

Referrlngrto FIGURE 2' there is illustrated diasrrna scanning aerial 51 and a receiver 52, feeding a display 53 havinga cathode ray tube 54. This display is of the fixed coil type as described with reference to FIG- URE l.l

Referring to FIGURE 2, the target position might be represented by voltages derived from a target position signal generator such as that shown at 2d, FIGURE 1. In FIGURE 2 however a more complex arrangement employing rate-aiding is illustrated so that there is no need for manual'control of a target position signal generator. to follow the movement of the vehicle. In the arrangement of FIGURE 2 there is illustrated an initial position' signal generator 6h which is set in accordance with the initial position of the vehicle when the. apparatus is brought into use and which generates two direct voltages representative of the co-ordinate position of thevehicle and a speed and direction signal generator 61 for generating direct voltages representative of the components of the speed of the vehicle in two co-ordnate directions. A target marker interscan trace is produced on the screen of the tube 54 by feeding the outputs from the signal generator 6@ to the shift control inputs of'two Waveform generators 62, 63 while the outputs from the signal generator 61 are fed to the scan control inputs of the waveform generators 62', 63. These waveform generators are arranged to generate linearly varying voltage waveform outputs having slopes proportional to the two speed components'and having starting points dependent on theoutput from the signal generator 6i). These outputs from the waveform generator 62, 63 will thus be voltages' which will Vary slowly in accordance with the change of' position of the vehicle as determined by the speed and direction sety on the signal generator 6I. The arrangement thus forms a rate-aiding system so that output voltages are available continuously representative Vof the position of the vehicle Without any necessity of manualfollowin'g. Such a rate-aiding circuit is more fully described in the aforementioned specification of patentfapplication No. 695,789 now abandoned,4 The direct voltage outputs from the waveform generators 62, 63 may be arranged to control a marker on the cathode ray tube 54 and for this purpose they are illustrated as being applied to a scanning generator unit 65 which may be similar to the waveform generators IS, 16 and associated switching means of FIGURE l.

y For generating the required track line, there are providedtwoftrack Waveform generators 70, 71 which generate` respectively repetitive sychronised waveforms representative respectively of the two co-ordinate components defining the required track. If this track is v displayed on the screen of the tube 54, these waveforms might be obtained from the scanning generator 65. The scanning generator 65 however has to feed deliector coils which have some resistance and may be provided with damping resistors. The scanning generator 65 would, for this reason have a more complex waveform to compensate `for non-inductive component of the load and it is therefore preferred to provide separate waveform generators 70, 711 The same control signals which control these waveform generators may be used for controlling a, 1 55,968rv the deliection scanning generators but for clarity inthe' drawing, such circuits for effecting the deflection of the* cathode ray beam to produce an interscan" trace cor-l responding to the required track-'are omitted in FIGURE 2. Referring to FIGURE Sthere is illustrated'diagrammaticaily a plan position display "'on which is marked a required track '76 and the positionof `a vehicle 77.'

The latter is illustrated' as being marked by a circle target marker '78. The waveforms for the twodirections" of deilection to produce the required track 'I6-arcillustrated in FIGURES 4a and 4b at 79 andll'respectively. Thesetwo FIGURES 4a and 4b are diagrams illustrating the waveforms during'two interscan periods which periods are marked as A and B respectively. n Each n i n of these two interscan periods would occur between radarv display scans and there maybe other different marker signals put on during other interscanV periods. ForV simplicity, however, only the two periods A and Bare illustrated. Period A is the interscan period for producing;

the target marker 73 and the waveforms necessary to produce this target marker are-shown at Sl, 82, the phaseI quadrature modulation for making the small circle being omitted for clarity. Each of the waveforms '79,' 8th/S11 waveforms Si, 82 are lines of constant voltage through-Y out the interscan period. It will be appreciated that theV corresponding waveforms for feeding the deflection coils of the cathode ray tube would be Vcurrent waveforms VVand not voltage waveforms. For the required track line -7'65 the ratio of the waveform amplitudes 79, Stlvaries according to the slope of the line in theV appropriate co-ordinate direction. In practice such complex tracks-maygenerally be built up from linear waveforms having different slopes.

For determining the distance of the vehicle from the track line, in the arrangement of FIGURE 2 it is required to select a particular point on the track line, to sample the track waveform voltages at this pointand to compare these voltages with the voltages representative or the position of the vehicle. The sampling of the track waveform voltages is effected by means of pulse sampling demodulators 35, S6 which serve to sample and store voltages representative of the instantaneous v-alues of the waveforms occurring at instants determined by an input sampling pulse. A form of 'pulse sampling demodulator suitable for this purpose is described with reference to FIGURE 2 of the specification of the aforementioned patent application No. 678,890 now U.S. Patent 3,120,666. The outputs from the pulse samplingldemodulators 35, 36 are compared with.` the outputs from the waveform generators 62, 63 by comparison'. means similar to those employed in' FIGURE l and comprising two subtracting units EW, S8, two resolvers 89, 96 and'two combining units 91, 92. The resolvers S9, @il have lobe set in accordance with the direction of the track. In practice, however, they may be controlled manually in accordance with the direction setting of the speed and direction signal generator 6l' employed for the rate-aiding circuit. It will be readily apparent, however, that the resolvers might be controlled automatically inaccordance with the instantaneous direction of the required track, for example by pulse sampling, with pulse sampling demodulators, the scanning rate input signals for the track' waveform generators and using the ratio ofthe outputs of these pulse sampling demodulators to control the two resolvers.

No reference has yet beenmade as to the manner of of straight lines, the track waveform generators may com-v prise linear waveform generators to the rate of scan control inputs of which are applied, for each track waveform, a succession of constant direct voltages which may be provided by electronic switching of a number of direct voltage sources. To produce a curved track line using a linear waveform generator, the rate of scan control input must be varied and may be derived from another waveform generator.

The outputs from the combiners 91, 92 may be fed to indicators 93 and/or to a modulator 162 for a radio transmitter 163 in a manner similar to that illustrated in respect to FIGURE l.

For selecting the timing of the sampling pulse for the pulse sampling demodulators S5, S6 there is provided a timing waveform generator 94 producing during each interscan period a linear waveform such as is shown at 95 in FIGURE 4c. The output from the timing waveform generator 94 is compared in a coincidence comparator 96 with a direct voltage output from a circuit 97. The coincidence comparator 96 compares these two voltages and produces a pulse when the two are equal. Such a coincidence comparator might, for example, comprise a pair of grid-controlled electronic valves arranged as a longtailed pair, that is to say having a common cathode impedance of high value, and the two voltages to be cornpared applied to the control grids of these two valves. As is well known, one or other of these two valves will be conductive according to which has the higher grid voltage and there will be a rapid change-over as the output of the timing waveform generator passes through the point of equality within the output from the circuit 97. The change-over in one direction is selected and used to produce a short duration pulse. This may be done, for example, by differentiating the output at the anode of one of the two valves of the longtailed pair and applying the differentiated signal to a suitable pulse shaping network.

In the simplest form the circuit 97 might comprise a manually operable potentiometer which can be set to give any required output voltage within the range of variation of output of the waveform generator 9d. It is preferred, however, to apply rate-aiding to the signal to be compared with the output of the timing waveform generator 94 and in FIGURE 2 the unit 97 is illustrated as including a rate-aiding circuit comprising a waveform generator 98 arranged to generate a linearly varying voltage waveform having an initial starting position controlled by an adjustable input voltage from a source 99 and having a slope controlled by an adjustable input voltage from a source ldd. The source 99 is adjusted in accordance with the initial position of the vehicle and the source 100 is adjusted in accordance with the speed of the vehicle. The rate-aiding circuit 9S will thus produce a linearly changing waveform changing at a rate proportional to the speed of the vehicle and starting from a datum position dependent on the initial position of the vehicle. The timing of the pulseproduced by the coincidence comparator 96 will therefore gradually change at a rate dependent on the speed of the vehicle. This pulse is used as the sampling pulse for the pulse sampling demodulators 8S, 86 and the gradual change in the timing of this pulse corresponds to the movement of the vehicle along the track'line. In FIGURE 4d, there are illustrated the sampling pulses produced by the coincidence comparator 96 and it will be seen that these correspond in time to the intersection of the timing waveforms 9S with the sloping dashed line lill which represents the effect of the rate-aiding circuit 93. i

With the arrangement of FIGURE 2 the waveforms corresponding to the track line are sampled at a preselected point which is made to move along the track line. The sampled voltages are compared with the actual position of the vehicle and the differences are combined and resolved in such a manner as to provide an indication of the distance off the track and the distance from a preselected point along the track provided that the pulse sampling point is made to follow along the` track in accordance with the nearest position on the track to the actual position of the vehicle. It will be appreciated that errors in the rate of movement of the sampling point along the track will not cause any errors in the indicated distances if the track is straight and will only cause second order effects if the track is curved and hence they are not of great importance.

In the apparatus of FIGURE 2, if the speed of the Vehicle is constant along the whole track, then the track waveform generators 79, 71 are arranged to produce waveforms such that the track line trace 76 on the screen of the cathode -ray tube is produced with a uniform velocity of movement of the beam across the screen of the tube, and the rate-aiding circuit 98 and the timing waveform generator 94 are arranged to produce linear waveforms. In some cases, however, it may be required that the vehicle should move along the track at a nonuniform speed; for'example, an aircraft might be required at some stage to climb with a resultant reduced speed. By suitable choice of the waveforms from the track waveform generators 7i?, 7l so that the cathode ray beam moves at a correspondingly reduced speed in tracing out the track line 76 on the screen of the tube, a linear timing waveform generator 94 and ajlinear rate-aiding circuit 98 may still be employed.

In some cases, at a radar station, it may be preferred to use a simpler system than that illustrated in FIGURE 2 and to employ manual following for obtaining the required information about the position of the vehicle with respect to the course line. One such simplified arrangement is illustrated in FIGURE 5 in which there is shown a radar system illustrated diagrammatically as comprising a transmitter liti, a scanning aerial 1li and a receiver 112, the latter feeding signals to a display M3. This display is assumed to be of the ixed coil type described above and having provision for displaying interscan traces. The required track for the vehicle is indicated on the display as such an interscan trace by means of two track waveform generators lid, IE5, Voltages representative of the position of the vehicle are produced by a target position signal generator M6 which might comprise an automatic follow system as described with reference to FIGURE 2 or a manual system as described with reference to FIGURE l, The output of this 'target position signal generator lid comprises two voltages representing the co-ordinates of the position of the target and these are applied respectively to shift control inputs of two waveform generators ilf, Il. To the rate of scan control inputs of these waveform generators there are provided two direct voltages representative of the sine and cosine components of the speed of the vehicle and these are illustrated in FIGURE 5 diagrammatically as being obtained from a sine-cosine potentiometer Il@ which is energised from an adjustable voltage supply source llZtl. The voltage suppiy source l2@ is adjusted to a value corresponding to the speed of the vehicle and the sine-cosine potentiometer Il@ is adjusted in accordance with the direction of travel of the vehicle. The waveform generators Il?, IIS will thus produce repetitive sawtooth waveforms which are fed to the display lf3 to produce a further interscan trace in the form of a line trace extending from the position of the vehicle determined by the signal generator 116 in the direction determined by the setting of the sinecosine potentiometer M9. The interscan waveform peri- .od is of limited duration and hence the length of the lline trace on the screen of the tube will be determined by the magnitudes of the rate of scan control voltages and hence by the setting of the adjustable voltage supply source 1243. In operation the sine-cosine potentiometer 3119 is adjusted so that the line extends from the position of the vehicle to the nearest point on the required track and the adjustable voltage supply source l2@ is then adjusted so that the length of the line is such that it just reaches the displayed l 1 trackl line. adjustable yvoltage supply sourcellZtV then represents the distance of the vehicle from the track and may either be displayed on anindicatorlZl `or transmittedlto the vehicle, for example, by beinglapplied to a modulator 122l endof-thisiinterscan' trace which` starts from the target' position'. The-.co-ordinates of the end'of the. line'may bei determinedby pulselsampling and compared'with the coordinatesof aldatum-position along the lengthor" the track:.linelto'determinel the distance along the track from th'e' datumposition.

Wer claim: Y

l. Apparatus for controlling the navigationof a vehicle along a-'reqnired'track comprising two electrical waveform generators arranged to generate repetitive synchronised waveforms representativefofthe co-ordinates in plan position oitherequired grou-nd track for the vehicle, a voltage source, a sine-cosine potentiometer connected to said source, manually operable-voltage controlling means vfor controlling the voltage applied from said source to said sine-cosine potentiometer, and two comparator means for determining the differences between the output signals from the sine-cosine potentiometer and the corresponding co-'ordinate instantaneous output signals of said waveform generators at simultaneously occurring instants in the Waveform cycles and for providing from said determined differences an output'representative of the distance of the vehicle from said track.

2. Apparatus for controlling the navigation of a vehicleV along a required track comprising a radar system with'- a transmitter for radiating radio signals, a receiver for receiving echoes of the radiated signals from distant targets and a plan position cathode ray tube display for displaying the received echoes, signal generator means forgenerating signals representative of the co-ordinates of`l` the ground-position ofthe vehicle, two electrical waveform generators arranged to' generate repetitive synchronised waveforms representative of the co-ordinates in plan position ofthe required ground -track of the vehicle, electronic marker circuit means arranged to display, under the control of the signals from said signal generator means, a irst electronic marker on said cathode ray tube in a position corresponding to the co-ordinates represented by the output signals of said signal generator means and arranged to display, under the control ofthe signals from said waveform generators, a second electronic marker on said cathode ray tube in the form of a line trace representing the required ground track, and two comparator means for determining the differences between the signals from said signal generators and the corresponding co-ordinate instantaneous output signals of said 'Waveform generators at simultaneously occurring instants in the waveform cycles and for providing from said determined differences an output representative of the distance of the vehicle from said track.

3. Apparatus as claimed in claim 2 wherein said signal generator meanscornprises an adjustable speed signal generator, an adjustable course signal generator and means controlled'by the speed signal generator and course signal generator toproduce co-ordinate outputs representative of the changing position of the vehicle in accordance with the settings of the speed and course signal generators.

4. Apparatus as claimed in claim 2 wherein said comparator means comprise a repetitive pulse producing generator'producing a pulse inreach cycle of the waveform generators which changes in position in successive cycles at a predetermined rate and pulse samplingdemodulators controlled by said pulse producing generator to sample With this arrangement the output of the? l2 the outputs of said waveform generatorsY attime instants in the repetition cycle of the waveform generators which change slowly at saidpredetermined rate.

5. Apparatus for controlling/the navigation of a vehicle? along a straight lineftrack extending from adatum posi-l tion on'the ground in a predetermined direction comprising a vmarker signal generator'ior generatingsignals rep resentative of the co-ordinates of the ground-positiono the-vehicle, a datum position signal generator. for generatingsignals' representative of theco-ordinates-ofsaidf datunr position, subtractingcircuits for determining the,`

diterences of corresponding co-ordinate signal outputs ofsaid marker 4signal generator and-said datum position signal generator, Itwo resolvingmeans for resolvingfrespectively the-signals representativeofzthe two saidditierences components along the-track to providea second'output and'means-forindicating themagnitudes ofsaid first and second outputs.

6; Apparatus as claimedy in claim l5 and"comprising aradar system with a'tr'ansmitterV for radiating radiol signals, a-receiver for receiving echoesofthe radiatedsignals, a plan positioncathode ray display tube for displayingrthe received echoes and4 anelectronic marker system controlled by-'said marker signal generator for displaying on said cathode ray display tube a marker ltracein aposi-r tion corresponding to the co-ordinatesl represented by the output signals of said marker signal generator.

7,. Apparatus as claimed in claim'Sinvr combination' witha-radio transmitter arranged to transmitsignalsrepresenting said first and second outputs'fand areceiver on the vehicle for receiving the signals from-said radiotransmitter and'ior providingv output'signals on the Vehicle corresponding to said irst and second outputs.

8. Apparatus -for controlling' the navigation of'a-'veiiclealong a required track comprising two electrical waveform' generators arranged to generatel repetitivesynferencesfbetween the signals representativerof the co-ordinates of the vehicle position and-thecorresponding coordinate signals from said pulse.samplinggdemodulators;

9. Apparatus as claimed in claim 8 wherein there are provided two resolvingmeans for resolving respectively the signals representative of saididiierences into components along and at right anglesto a predetermined direction, and two combining means forV combining the two resolved components in said direction to provide alirst output and for combining'thetwo resolved components at right vangles to said direction to provide a-second output.

l0. In apparatus for controlling the navigation ofil a a vehicle; the combination oftwoelectrical waveform generators arranged to generate repetitive synchronised waveforms representative of the co-ordinates in plan position of the required ground trackv for thevehicle, a timingwaveform generatorr producingfa repetitive'linearly varyingV sawtooth waveform synchronised withf the output of'said electrical waveform generators, a control sig-` nal generator producinga signal varying in `amplitude'at a predetermined rate over a period containingmany cycles of the'output of said electrical waveiornr genera- 13 tors, comparator means arranged to produce an output pulse each time the output of said timing waveform generator bears a predetermined amplitude relationship to the output of said control signal generator, and two pulse sampling demodulators controlled by said comparator means to sample simultaneously the synchronised waveforms from said electrical waveform generators to produce signals representative of the co-ordinates of a point on said ground track. i

1l. The combination as claimed in claim 10 wherein said control signal generator comprises a linearly varying waveform generator with adjustable means for controlling the rate of variation of the linearly-varying signal output.

12. The combination as claimed in claim 1l wherein said adjustable means are provided on said control signal generator for controlling the datum level of the start of the linearly-varying signal output.

13. In radar apparatus having a plan position radar display on a cathode ray tube with orthogonal deector means; apparatus for controlling the navigation of a vehicle comprising an electronic marker system producing two marker signal outputs representative of theV two cordinates of a position in a rectangular co-ordinate system, means for applying said marker signal outputs to said orthogonal deector means to produce a marker on said display, control means for said marker system to make said marker track on said display follow the radar response from said vehicle, two electrical waveform generators arranged to generate repetitive synchronised waveforms representative of the co-ordinates in plan position of the required ground track for the vehicle, two pulse sampling demodulators arranged to sample said synchronised waveforms simultaneously to produce signals representative of the co-ordinates of a point on said track, control means for said pulse sampling demodulators arranged to control the timing of the sampling pulses so that the sampling points occur at instants in successive cycles changing progressively at a predetermined rate, and two comparator means for determining the diierences between the marker signal outputs representative of the co-ordinates of the position of the tracking marker and the corresponding co-ordinate signals from said pulse sampling demodulators.

14. Apparatus as claimed in claim 13 wherein said control means for said pulse sampling demodulators cornprises a timing waveform generator producing a repetitive linearly varying sawtooth waveform synchronised with the output of said electrical waveform generators, a control signal generator producing a signal varying in amplitude at a predetermined rate over a period containing many cycles of the output of said electrical waveform generators, comparator means arranged to produce an output pulse each time the output of said timing waveform generator bears a predetermined amplitude relationship to the output of said control signal generator, and means for applying said output pulse to said pulse sampling demodulators to control the times of the sampling pulses.

15. Apparatus as claimed in claim `13 wherein said electronic marker system comprises an adjustable speed signal generator arranged to produce two rate control signals representative respectively of the two components of a selected speed in a selected direction, an adjustable initial position signal generator for producing datum control signals representative of the co-ordinates of a selected datum position, and a pair of electrical waveform generators controlled by said speed signal generator and said initial position signal generator to produce each a linearly varying waveform Varying slowly over many cycles of said repetitive waveforms at rates controlled by the respective rate control signals and starting from levels controlled by the respective datum control signals.

16. In apparatus for the radar control of a vehicle along a selected track; the combination of means for producing a first pair of signals representative of the coordinates of the actual position of the vehicle in a rectangular co-ordinate system, means for producing a second pair of signals representative of the co-ordinates of the scheduled position on said track in the same coordinate system, two subtracting means for producing signals representative of the differences, in the two coordinate directions respectively, of the signals of said tirst and second pair, a pair of resolving means arranged to resolve the difference signals in a predetermined direction and at right angles thereto, and a pair of combining means arranged to combine respectively the two resolved components in said predetermined direction andthe two resolved components at right angles to said predetermined direction.

17. Apparatus for controlling the navigation of a vehicle comprising rst signal generator means arranged to generate electrical signals representative of the Cartesian coordinates of the instantaneous position of the vehicle, further signal generator means arranged to generate two sets of repetitive synchronised waveforms the amplitudes of which are linearly dependent on the coordinates which define a required track in the said coordinate system, and computing means responsive to the signals from said first signal generator means and the signals defining the required ground track to provide an output representative of the distance of the point represented by signals from said first signal generator means from the track defined by the output of said further signal generator means.

18. Apparatus for controlling the navigation of a vehicle when the required track in plan position is a straight line comprising rst signal generator means arranged to generate two signals representative in Cartesian coordinates of the plan position of the vehicle, further signal generator means arranged to provide two signals representative of the coordinate position in the same coordinate system of a point on the required ground track and also at least one signal representative of the angular direction of the required ground track and computing means, responsive to the signals from rst signal generator means and the signals defining a required ground. track and arranged to determine the differences between the outputs from said rst signal generator means and the corresponding outputs from said further signal generator means representative of said point, resolving means controlled in accordance with said signal representative of the angular direction of the required ground track arranged to resolve said differences into components along and transverse to the track and combining means to combine the resolved components transverse to the track to provide an ouput representative of the distan-ce of the vehicle from said track.

19. Apparatus as claimed in claim 18 wherein there are also provided combining means to combine the resolved compouents along the track to provide an output dependent on the distance of the vehicle along said track from'said point.

20. Apparatus for controlling the navigation of a vehicle along a required track comprising electrical waveform generators arranged to generate repetitive synchronized waveforms whose amplitudes are linearly dependent on the Cartesian coordinates defining the required ground track in plan position, signal generator means arranged to generate electrical signals representative of the coordinates in plan position of the instantaneous position of the vehicle in said coordinate system and comparator means for determining the difference between the signals representative of the vehicle position vand the corresponding coordinate instantaneous output signals of said waveform generators at simultaneously occurring instants in the waveform cycles and for providing from said determined differences an output representative of the distance of the vehicle from said line.

21. Apparatus for controlling the navigation along a required track comprising electrical waveform generators arranged to generate repetitive synchronized waveforms J T5 whose amplitudes are linearly'dependent on the Cartesian coordinates dening the required ground track in plan position, signal generator means arrangedl to generate electrical signals representative of the coordinates of the instantaneous plan positionof the vehicle in said .coordinate system and comparatormeans for including pulse sampling demodulators for sampling and storing voltages representative of the required instantaneous output sig nals of the waveform generators at simultaneously 0ccurring instants in the waveform cycles of said waveform generators, rneansfor obtaining difference signals in the coordinate directions between the signals representative of the'vehicle position and the sampledvoltages and resolving andrcombining means controlled inaccord#Y aidingcircuitvisprovided-for controlling the instant of' f sampling of. said pulse sampling. demodulators so that the sampling Vpoint traversesalong the-.track at an adjustable ratewhich moyfbeset-to correspond tothe speedof the vehicle.

,References Cited'iu the le of this patent UNITED STATES PATENTS' 2,480,068 Wolff Aug. 23, 1949- 2,535,107 WallaceVarnaa; Dec. 26, Y1950 2,582,588A Fennessy Jan.- 15, 19'52" 2,584,599 Luck Feb. 5,3 1952.`- 2,741,760 Franke vApr. 10,-1956" 2,980,902 Tasker Apr.' 18,` 1961 3,071,765 Schutz..V Jan. 1,- 1963"k 

1. APPARATUS FOR CONTROLLING THE NAVIGATION OF A VEHICLE ALONG A REQUIRED TRACK COMPRISING TWO ELECTRICAL WAVEFORM GENERATORS ARRANGED TO GENERATE REPETITIVE SYNCHRONISED WAVEFORMS REPRESENTATIVE OF THE CO-ORDINATES IN PLAN POSITION OF THE REQUIRED GROUND TRACK FOR THE VEHICLE, A VOLTAGE SOURCE, A SINE-COSINE POTENTIOMETER CONNECTED TO SAID SOURCE, MANUALLY OPERABLE VOLTAGE CONTROLLING MEANS FOR CONTROLLING THE VOLTAGE APPLIED FROM SAID SOURCE TO SAID SINE-COSINE POTENTIOMETER, AND TWO COMPARATOR MEANS FOR DETERMINING THE DIFFERENCES BETWEEN THE OUTPUT SIGNALS FROM THE SINE-COSINE POTENTIOMETER AND THE CORRESPONDING CO-ORDINATE INSTANTANEOUS OUTPUT SIGNALS OF SAID WAVEFORM GENERATORS AT SIMULTANEOUSLY OCCURRING INSTANTS IN THE WAVEFORM CYCLES AND FOR PROVIDING FROM SAID DETERMINED DIFFERENCES AN OUTPUT REPRESENTATIVE OF THE DISTANCE OF THE VEHICLE FROM SAID TRACK. 